The present invention relates generally to the field of separating and removing particulates from gas streams. In particular, the invention relates to an electrostatic particulate separation system for separating and removing particulates from gas streams.
Conventional methods of removing particulates, such as ash and dust, from a gas stream include using barrier filters such as fabric filters and baghouses, electrostatic precipitators, or cyclonic separators. Each of these approaches has its specific limitations that will be described briefly in turn.
Barrier filters typically induce significant pressure drops that translate into significant parasitic losses. In retrofit applications, accommodating the pressure drop caused by the filter may require costly modification of plant fans. In addition, filters have a limited life and must be replaced at regular intervals, resulting in increased operational costs and downtime.
Electrostatic precipitators (ESP) are particularly effective at high particulate loadings. However, at low loadings and for small particle diameters, the separation efficiency may be much lower. Thus, if very low outlet particle concentrations or capture of small diameter particles is required, the size and cost of the ESP can increase very significantly. ESPs also require that the collected particulates be periodically cleaned from the collection plates, typically through rapping, in order to maintain the efficiency of the system. This rapping can produce a temporary increase in the particulate concentration at the ESP outlet, thus limiting the minimum average outlet concentration that can be achieved.
Cyclonic separators do not require cleaning and can thus operate continuously. However, cyclonic separators are typically only effective for larger diameter particulates and result in significant pressure drops, leading to parasitic losses in the system.
Examples of electrostatically enhanced separators currently used in the art are described in U.S. Pat. Nos. 5,591,253 and 5,683,494 (Altman et al.), which are hereby incorporated by reference.